Computer Networks · Exam Notes

Difference between OSI and TCP/IP Model

Exam-focused notes on the OSI model vs TCP/IP model for SSC, Banking (IBPS/SBI), Railway, UPSC, NIELIT, JAIIB/CAIIB and IT officer papers. Learn layer counts, functions, mapping, protocols, PDUs, key differences, and practice with interactive MCQs.

OSI 7 layers TCP/IP 4 layers Mapping table 60 MCQs

Why Two Models?

Both explain layered communication — different goals

Must Know

Network communication is complex, so we split it into layers. Two famous models are:

OSI Model

7 layers · theoretical / reference · by ISO · best for teaching

TCP/IP Model

4 layers · practical Internet suite · by DARPA · used in real networks

Exam line: OSI = how to understand networks. TCP/IP = how the Internet actually works.

Difference between OSI and TCP IP model diagram

OSI Model — 7 Layers

Open Systems Interconnection · ISO reference model

Very Important

#	Layer	One-line job	Examples / notes
7	Application	User network services	HTTP, FTP, SMTP, DNS, Telnet
6	Presentation	Translate, encrypt, compress	Data formats, SSL/TLS concepts (exam view)
5	Session	Start / manage / end sessions	Dialogue control, checkpoints
4	Transport	End-to-end delivery, ports	TCP (reliable), UDP (fast)
3	Network	Logical addressing & routing	IP, ICMP, routers
2	Data Link	Frames, MAC, error detection on link	Ethernet, switches, bridges
1	Physical	Bits & signals on media	Cables, hubs, repeaters, NICs (signal)

Mnemonics: Top→bottom: All People Seem To Need Data Processing. Bottom→top: Please Do Not Throw Sausage Pizza Away.

TCP/IP Model — 4 Layers

Practical Internet protocol suite

Very Important

Layer	Main job	Key protocols
Application	User services + presentation/session roles combined	HTTP/HTTPS, FTP, SMTP, DNS, DHCP, SNMP
Transport	Host-to-host delivery, ports, reliability options	TCP, UDP
Internet	Logical addressing, routing across networks	IP, ICMP, IGMP, ARP-related delivery support
Network Access (Host-to-Network)	Physical network connection / framing	Ethernet, Wi-Fi, PPP, etc.

Note: Some books show TCP/IP as 5 layers by splitting Network Access into Data Link + Physical. Exams usually accept 4 layers.

OSI ↔ TCP/IP Layer Mapping

Most important comparison skill for MCQs

OSI layers	TCP/IP layer
Application + Presentation + Session	Application
Transport	Transport
Network	Internet
Data Link + Physical	Network Access

Missing as separate TCP/IP layers

Session and Presentation are not separate in TCP/IP — their jobs sit inside Application.

Name change to remember

OSI Network ≈ TCP/IP Internet (IP & routing).

Key Differences (Exam Table)

Revise this the night before

Feature	OSI Model	TCP/IP Model
Layers	7	4 (sometimes 5)
Developed by	ISO	DARPA / DoD
Nature	Theoretical / reference	Practical protocol suite
Protocol dependency	Protocol-independent	Protocol-specific (TCP, IP, HTTP…)
Session & Presentation	Separate layers	Merged into Application
Usage today	Teaching, design reference	Real Internet implementation
Modularity	Highly modular for learning	Less strict separation
Examples focus	Conceptual layer roles	Real protocols & services

History tip: TCP/IP work existed before OSI became a standard — common true/false MCQ.

PDU Names (Bonus High-Yield)

Common PDUs

Application: Data / message
Transport: Segment (TCP) / Datagram (UDP)
Network/Internet: Packet / IP datagram
Data Link: Frame
Physical: Bits

Device ↔ layer quick map

Hub / Repeater: Physical
Switch / Bridge: Data Link
Router: Network / Internet
Gateway / Proxy (often): upper layers

One-Glance Quick Revision

OSI layers

7 · ISO · reference

TCP/IP layers

4 · DARPA · Internet

OSI top 3 →

TCP/IP Application

OSI Network →

TCP/IP Internet

OSI L2+L1 →

Network Access

No separate in TCP/IP

Session, Presentation

TCP/UDP

Transport

IP

Internet / Network

HTTP/FTP/SMTP/DNS

Application

Router

Layer 3 / Internet

Switch

Layer 2

Hub

Layer 1

Practice MCQs — OSI vs TCP/IP

Tap any option to reveal the correct answer and a short explanation.

60 Questions

Exam Tips

Remember the numbers first

OSI = 7, TCP/IP = 4. That alone clears many questions.

Map before you panic

If a question mixes names (Internet vs Network, Network Access vs Data Link), draw the mapping table mentally.

Reference vs real

Teaching/reference → OSI. Internet/practical protocols → TCP/IP.

Missing layers trick

Session and Presentation are OSI-only as separate layers.

Protocol placement

HTTP/FTP/SMTP/DNS = Application. TCP/UDP = Transport. IP = Network/Internet.

Device placement

Hub L1, Switch L2, Router L3. Don’t put routers at Application.

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